This invention is related to U.S. Pat. No. 3,915,220; and U.S. Pat. No. 4,050,512, which are for tools connected to drill pipe and lowered down an oil well to test the formation reservoir; whereas the present invention is arranged for installation at an end of a drill kelly, and is summarized in the following objects:
First, to provide a kelly valve structure, which, with a minimum change in parts, may be installed at the lower end of a drill kelly to prevent spillage of mud from the kelly onto the derrick floor when the drill string is being disconnected; or, may be installed at the upper end of the drill kelly to close automatically and stop reverse flow from the drill string, thereby serving as a blow out preventor.
Second, to provide a kelly valve structure, which, when installed at the lower end of the drill kelly and subjected to low pressure existing during connection of the drill string to the kelly or disconnection therefrom, automatically opens in response to the increased drilling fluid pressure established upon resumption of drilling, and thus functions as an anti-spillage valve.
Third, to provide a kelly valve structure which, when installed at the upper end of the drill kelly and subjected to excessive pressure in the drill string is caused to shut off completely and serve to prevent blow outs, and thus serve as a safety valve.
Fourth, to provide a kelly valve structure, including a novelly arranged ball valve, which not only is rotatable between an open and a closed position, but also is axially movable in response to line pressure, when in its closed position, to bypass well fluid to equalize or reduce pressure differential across the valve.